1. Field of the Invention
The present invention relates to an optical disk recording device which executes data reproduction and recording from and on an optical disk medium and, more particularly, to an optical disk recording device capable of monitoring of a reproduced signal being recorded even when laser power is increased during data recording.
2. Description of the Related Art
Conventional optical disk recording devices which conduct optical reading and recording of information are provided with a reproduced signal photo detector for detecting reflected light from an optical disk medium in order to monitor a reproduced signal at the time of recorded data reading and at the time of data recording. The optical disk recording devices are also provided with an amplifier for amplifying a reproduced signal read from the optical disk medium because reproduction power at the recorded data reading is lower than recording power. Amplification degree of this amplifier is fixed in general.
In addition, conventional magneto-optical disk recording devices require verification to be conducted after data recording for the purpose of ensuring data reliability because the devices lack in an overwrite function which a magnetic recording device has and because the devices are liable to have a defect such as adsorption of refuse and scratches. Therefore, the devices have a drawback that they are slow in recording operation by a time for waiting for disk rotation. More specifically, the current optical disk recording devices need three steps (time for three rotations of a disk) of data erasing, data recording and verification of recorded data. The magneto-optical disk recording devices conduct verification of recorded data by monitoring a reproduced signal during data recording.
FIG. 9 shows common structure of a conventional optical disk recording device. In FIG. 9, this optical disk recording device includes a semiconductor laser diode (LD) 900, a recording current drive circuit 901 for supplying the semiconductor laser diode 900 with a recording current, a convergent lens 902, an objective lens 903, a half prism 904, a recording gate circuit 905, a reproduced signal photo detector 906 as an optical information detector, a pre-amplifier 907 and a recording state discrimination circuit 908. 100 denotes an optical disk medium, 1001 recording data and 1002 recording beam.
The recording beam 1002 from the semiconductor laser diode (LD) 900 is irradiated onto the optical disk medium 1000 and the reflected light is detected to read data. In data recording, the recording gate circuit 905 enters an ON state to apply a recording gate signal to the recording current drive circuit 901, so that power of the recording beam 1002 from the semiconductor laser diode (LD) 900 is increased.
As described in the foregoing, the conventional optical disk recording devices have a constant amplification degree of an amplifier which amplifies a reproduced signal from a reproduced signal photo detector and are therefore provided with no function of controlling an amplification degree of the amplifier such that a reproduced signal output from the reproduced signal photo detector during data reading and a reproduced signal during recording when the amount of incident light is increased have a predetermined level. As a result, if laser power increases at the data recording when the recording gate circuit enters the ON state, as the amount of light incident on the reproduced signal photo detector is increased, a reproduced signal from the reproduced signal photo detector is increased. Then, when the reproduced signal from the reproduced signal photo detector is amplified at the amplifier, saturation of a reproduced output signal will occur. In this case, there arises a problem at an on-recording verification device which conducts recording verification by using a reproduced signal being recorded that precise monitoring of a reproduced signal being recorded is impossible.
In conventional optical disk recording devices which conduct no recording verification, no consideration is given to a means for switching an amplification degree of a reproduced signal output circuit of a photo detector because monitoring of a reproduced signal being recorded when a recording gate circuit enters the ON state to increase laser power is unnecessary.
Conventional built-in amplifier reproduced signal photo detector which is provided with no means for controlling an amplification degree of an amplifier for a signal with a large input amplitude has a shortcoming that another reproduced signal photo detector as a countermeasure against saturation of a reproduced signal should be prepared, which can not be coped with addition of inexpensive and simple components.
For changing an amplification degree of an amplifier when light power is changed at an optical disk recording device, conventionally employed is a method of providing an AGC (automatic gain control) circuit within a servo loop in order to obtain stable servo operation at the time when laser power for data recording becomes higher than that of the reproduction, thereby correcting a loop gain so as not to be changed even with a change of the amount of reflected light from an optical disk due to a change of the laser power or a change of a reflectance of the optical disk. Conventional AGC circuits, however, make an output constant by feeding back an unsaturated input signal and therefore can not be employed without modification as a technique of amplifying a reproduced signal according to the size of a reproduced signal at the data reading and the size of an increased reproduced signal being recorded within a range in which no saturation of output will occur to catch and monitor a subtle response of the reproduced signal.